Reef manta ray description

A very large, graceful ray, the reef manta ray (Manta alfredi) is a distinctive fish with triangular pectoral ‘wings’ and paddle-like lobes which extend in front of the mouth (4)(5). Known as cephalic lobes, these are forward extensions of the pectoral fins which form a funnel-like structure while feeding, helping to channel plankton-rich water into the mouth (3)(4)(5). The cephalic lobes are rolled into a spiral when the reef manta ray is swimming (5).

Although smaller than its close relative the giant manta ray (Manta birostris), the reef manta ray still grows to an impressive size. Females are around a third larger than males, probably as an adaptation to allow them to give birth to large pups (3).

The disc-like body of the reef manta ray is just over twice as wide as it is long, and ends in a slender, whip-like tail (2). There is a small dorsal fin on the reef manta ray’s back (5). The broad, rectangular mouth is located at the front of the head and has rows of tiny, peg-like teeth on the lower jaw (4)(5), while the eyes are located on the side of the head and the gills open on the underside of the body (5).

The reef manta ray is quite variable in appearance, but most individuals belong to a ‘chevron morph’, which is mainly black above and white below, with large white ‘shoulder’ patches. The white patches form a ‘Y’ shape on top of the reef manta ray’s head, and fade into the black of the back (2)(3). There may also be pale colouration on the tips of the pectoral fins(2).

The underside of the reef manta ray is predominantly cream to white, with variable numbers of black to blue-grey spots (2)(3). These spots vary in size and can be seen across most of the underparts, although most patterning occurs between the gills, on the abdomen and across the rear half of the pectoral fins. There are also pale to dark charcoal-coloured bands on the rear edge of the pectoral fin, while the reef manta ray’s mouth is white to light grey (2).

A ‘black morph’ of the reef manta ray also occurs, which is completely black above and almost totally black below, except for a white patch of variable size around the gills and on the abdomen. Black spots can often be seen within this white patch (2)(3). ‘Chevron’ mantas that appear almost entirely white from above have also been observed (2). Reef manta rays vary considerably in their spot patterns and in the patterning on the back, and this, together with unique patterns of scars, can be used to identify individuals (3)(4)(5).

Although previously considered to be a single species, manta rays have now been divided into two distinct species, the reef manta ray and giant manta ray, based on differences in size, appearance, habitat, behaviour and genetics (1)(2)(3). As well as being smaller, the reef manta ray lacks the non-functional tail spine of the giant manta ray, and its white shoulder patches form a ‘Y’ rather than a ‘T’ shaped pattern. The white patches also fade into the black of the back rather than being distinct. Reef manta rays also differ in having spots across the whole of their underside, and in having a white or grey rather than black mouth (2)(3).

Studies have suggested that a third species of manta ray may exist, but more evidence is needed before the species can be split further (1)(2).

Related species

Reef manta ray biology

A graceful swimmer, the reef manta ray almost appears to fly through the water as it flaps its large pectoral fins. However, it is also capable of rapid speed, and individuals sometimes leap clear of the water, landing with a loud slap. Several of these jumps may be performed in succession, and they could potentially function to remove parasites, escape a predator, communicate with other individuals, or even be a form of play (4)(5).

Despite its massive size, the reef manta ray feeds on tiny planktonic organisms, which it filters from the water using plates of sponge-like tissue between the gills, known as gill rakers (3)(4)(5). As the reef manta ray feeds, the cephalic lobes on either side of the head are unfurled and help direct water into the mouth (4)(5). Manta rays often perform slow somersaults in the water as they feed, and sometimes also scoop plankton up along the sea floor (3)(4)(5).

The reef manta ray often aggregates in large numbers when feeding, and has also been seen to travel in groups (1). Manta rays often play host to smaller fish called remoras, which attach to the ray’s body and consume particles of food that fall from its mouth. The reef manta ray regularly visits ‘cleaning stations’ where fish such as wrasses (Labroides spp.) pick parasites off its body (3)(4)(5).

During courtship, one or more male reef manta rays chase a female around the reef as they compete for the right to mate. Eventually, the successful male grasps the tip of one of the female’s pectoral fins between its teeth (3)(4)(5), with this species almost always choosing the left pectoral fin(7). The pair mate belly-to-belly, and fertilisation is internal, with the male transferring sperm to the female using a pair of ‘claspers’ on the inner part of the pelvic fins(4).

The eggs of the reef manta ray develop inside the female’s body for up to a year (3)(4)(7) and then hatch internally, so that the pups are born live (4). Usually only a single pup is born at a time, although occasionally two have been observed (1)(3)(4)(7). In some parts of its range, the reef manta ray gives birth in the summer (7), while in other areas breeding behaviour appears to be more common in the winter months (8)(9). Births apparently take place in shallow water and at night (3).

The newborn reef manta ray already measures an impressive 1.5 metres across (2)(3), and grows rapidly, almost doubling in size during the first year of life (4). The size at which the reef manta ray becomes sexually mature varies across its range, but males are generally thought to mature when the disc-like body measures about 2.5 to 3 metres across, and females at about 3 to 3.9 metres (1)(2)(3), corresponding to an age of around 8 to 15 years (1)(3). Although larger females are capable of giving birth in consecutive years, most female reef manta rays give birth only once every two to five years (1)(7)(8).

The exact lifespan of the reef manta ray is not yet known, but it is believed to live for at least 40 years or more (1). The only known predators of manta rays are large sharks (4)(5)(9), orcas (Orcinus orca) and false killer whales (Pseudorca crassidens) (3).

Reef manta ray range

The reef manta ray is found in tropical and sub-tropical waters in the Pacific and Indian Oceans. However, within this widespread range its populations appear to be quite patchy (1).

This species is quite widespread in the Indian Ocean, from the Red Sea in the north to South Africa in the south, and from Thailand southwards to Western Australia. It is also found in the western and southern Pacific, east to French Polynesia and Hawaii (1)(2).

The reef manta ray is believed to have a smaller distribution than the giant manta ray (2)(3). It is also less migratory, tending to remain resident in more tropical waters and in specific locations, which gives rise to its alternative name of ‘resident manta ray’ (1)(3).

Species with a similar range

Reef manta ray habitat

A less oceanic species than the giant manta ray (2), the reef manta ray is more commonly found in shallow inshore waters. It typically occurs around coastal reefs, tropical island groups, atolls, bays and productive coastlines (1)(2)(3), but may also be seen around offshore reefs and seamounts (1).

The reef manta ray is usually resident in a specific home range, often visiting the same sites year after year (3). However, although less migratory than the giant manta ray, this species does undertake seasonal movements as it follows changes in food abundance (1). For example, in the Maldives the reef manta ray moves to different areas as monsoon currents switch direction at different times of year, altering the distribution of its plankton prey (6).

Reef manta ray status

Reef manta ray threats

Although the reef manta ray is widespread, its populations appear to be quite patchily distributed and fragmented. Its overall population size is unknown, but most individual populations seem to be small, and overall the species is in decline (1).

Manta rays are quite easy to catch due to their large size, relatively slow swimming speed, and tendency to be found at the water’s surface at predictable locations (1)(3). Although historically hunted for their meat, skins and liver oil (3)(4), manta rays have more recently become highly valued for their gill rakers, which are used in the Chinese medicine trade (1)(3). In addition, many manta rays are taken as bycatch in other fisheries or become entangled in fishing lines and nets (1)(3), including bather protection nets used in shark control (1).

As well as causing direct mortality, entanglement in fishing gear can also cause severe injuries. For example, one in ten reef manta rays studied off Maui, Hawaii, had amputated or injured cephalic fins due to entanglement in fishing line, potentially affecting their ability to feed (9).

Further threats to the reef manta ray may include collisions with boats, habitat degradation, pollution, ingestion of plastic particles and climate change (1). Due to its more coastal distribution, the reef manta ray is likely to be more vulnerable than the giant manta ray to near-shore human impacts, such as coastal development, pollution and storm water run-off, particularly as it often remains resident in a specific area (9).

Of increasing concern to the reef manta ray is a rise in dive tourism, which if not properly managed may negatively affect manta ray behaviour and potentially damage their habitat (1)(4)(5)(9)(10). Recent success in breeding manta rays in captivity has also sparked a global interest from aquariums in acquiring specimens. This may have the potential to result in unsustainable taking of individuals from the wild (9).

The reef manta ray’s slow birth rate makes it particularly vulnerable to overexploitation, and its populations are slow to recover from any declines (1)(3)(4)(9).

Reef manta ray conservation

International protection for the reef manta ray is still poor (3). However, some countries have established national protection for this species, with fishing of manta rays now banned in Hawaii, the Philippines and the Maldives (1)(3)(9). In Western Australia, the reef manta ray is protected from fishing and disturbance within marine parks (1), and in the Maldives two Marine Protected Areas have been set up specifically to protect manta rays (1)(3)(9). A Marine Protected Area for manta rays has also been established around the island of Yap, in the western Pacific Ocean (1)(9).

Dive tourism is a growing industry, and is likely to help the conservation of the reef manta ray by making it worth more alive than fished (1)(3)(10). For example, manta ray watching in the Maldives has been estimated to be worth about US$8.1 million a year, and helps support both research and conservation (10). However, any tourism activities need to be carefully managed and regulated to prevent them having negative impacts on reef manta ray populations (1)(3)(10). Codes of conduct are already in place in some countries (9).

In 2011, the Manta Trust was formed to co-ordinate global research and conservation efforts for manta rays (3). A number of studies have been undertaken using photographic identification as a way of monitoring reef manta rays (7)(9)(11), although much still remains to be discovered about this species’ biology and behaviour (3)(9). The separation of manta rays into two distinct species will allow more appropriate management decisions to be made, based on differences in their behaviour, habitat use and life histories (2)(3).

Manta rays are large and charismatic species, and as such can act as ‘flagship species’, helping to promote conservation and encourage the protection of the wider marine environment (3).

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